Metallurgical furnace lining and method of production

ABSTRACT

This invention relates to bricks and other refractory bodies for lining metallurgical equipment such as blast furnaces which are made resistant to alkali attack by impregnation with phosphorus compounds.

United States Patent [191 Owen et a1.

[73] Assignee: Koninklyke Nederlandsche Horgovens En StaalfabriekenN.V., ljmuiden, Netherlands [22] Filed: Dec. 7, 1970 [21] Appl. No.:95,986

Related US. Application Data [63] Continuation-impart of Ser. No.766,644, Oct. 9,

1968, abandoned.

[52] 11.8. CI. ..106/56, 106/65, 106/67, 106/68, 106/69, 117/119,117/123 A,

[51] llnt. C1. ..B44d 1/02 Field of Search ..106/55, 67, 68, 69, 65, 56;264/30, 62, 66, 118; 117/114, 123 A, 169 R 1 3,708,317 [451 Jan.2,1973

[56] References Cited UNITED STATES PATENTS 2,805,174 9/1957 Veale..117/54 3,357,842 12/1967 Bowman ..264/30 X OTHER PUBLICATIONS TheCondensed Chemical Dictionary, 7th Edition, Reinhold Publishing Corp.,New York, Copyright 1950, 1956, 1961 Primary Examiner-Edward G. WhitbyAttorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT This inventionrelates to bricks and other refractory bodies for lining metallurgicalequipment such as blast furnaces which are made resistant to alkaliattack by impregnation with phosphorus compounds.

13 Claims, No Drawings METALLURGICAL FURNACE LINING AND METHOD OFPRODUCTION This application is a continuation-in-part of applicationSer. No. 766,644 filed by us on Oct. 9, I968, now abandoned.

The invention relates to a metallurgical furnace, more specifically ablast furnace, for the preparation of a molten metal in the presence ofalkali metal compounds.

The invention further relates to a refractory body such as bricks, and amethod of making them for use as lining material in blast furnaces andlike metallurgical equipment where alkali-attack can take place.

The object of the invention is to provide metallurgical furnaces, inparticular blast furnaces, the refractory lining of which has a greaterresistance to the distinctive action of alkali metal compoundsregardless of whether or not this lining consists of oxides of aluminumand silicon or aluminum silicates, or carbon.

Another object of the invention is to provide refractory bodies forlining metallurgical furnaces, in particular blast furnaces, beingresistant to alkali attack.

The destructive influence of alkali metal compounds, particularlypotassium compounds, on the refractory material being used as lining inblast furnaces and like metallurgical equipment, is well-known torefractory technologists. This phenomenon, being generally referred toas alkali attack, occurs not only with refractory lining consisting ofalumino, silica and/or alumino silicate, but also with refractory liningconsisting of carbon. It is immaterial whether this lining is present inthe furnace in the form of bricks or other refractory bodies or in theform of an uninterrupted, continuous, monolithic lining.

Alkali metal compounds are introduced into the furnace as minorconstituents of the raw materials charged to the furnace. In case of aniron-making blast furnace said compounds are introduced by the iron ore,the coke and particularly by the slag-forming additives. In marinedistricts alkali metal compounds may even be introduced by the hot blastair.

Under the reducing conditions under which the furnace operates, thesealkali metal compounds volatilize and partly accumulate in the lining,particularly in the lower regions of the shaft (where alkali contents upto about 30 percent may be found) and also in the bosh and the hearth.Because of the reaction which takes place between said alkalies and therefractory material of the lining, considerable disruption of saidmaterial is caused, and consequently, the useful life thereof ismaterially shortened.

This disruption occurs irrespective of whether or not the variousrefractory lining materials, being used for different parts of thelining, originally had excellent physical properties with respect toerosion, corrosion and abrasion resistance, or good resistance tomechanical stressing, slag attack and thermal shock.

The alkali attack also occurs in the linings of other furnaces in whichthere is a reducing atmosphere, e.g., furnaces for the reduction of oressuch as those of copper and zinc.

The reaction with the refractory material takes place with the alkaliesin both the gaseous and the liquid phase, but said reaction proceedsmuch quicker in the liquid phase. Therefore, the alkali attack becomesmuch worse when the volatilized alkalies condensate on or inside therefractory lining material.

Until now the refractory technologist was confronted with the problemthat the alkali attack occurs not only on the external surface of therefractory material, but also on the internal surface thereof since thealkali penetrates internally into the refractory material, especiallywhen said material is porous. This internal attack causes a destructiveaction both on the refractory material and on the bonding which holdsthe refractory grains together. Because of this internal attack, thereis a rapid loss of refractory material.

When alumino silicates or high-alumino is used as the refractorymaterial, the alkalies react withsaid material to form compounds such aspotash feldspar (K O-Al O '6S iO leucitel(K O-AlO'-4SiO), kaliophilite(K O'Al O '2SiO and B-alumina (K 012 AI O Other compounds may be formed,such as compounds in which the K 0 is partially replaced by N320.

The specific volume of the reaction products formed by the alkali attackon the refractory lining material is generally greater than the volumeof the reacting substances themselves. Consequently the alkali attackleadsto disruptive stresses within the refractory material causing atleast a serious cracking of the material. It is common to find that thecoherence of the refractory lining material in a blast furnace that hasbeen in operation for some time is completely destroyed by this increasein volume.

The disruptive action of the reaction which takes place during thealkali attack proceeds irrespective of the favorable properties of therefractory lining, being used in furnaces for the first time, so thatimprovements made in the strength of the refractory material do notsolve the problem of alkali attack.

Another object of this invention is to provide a method of makingrefractory bodies such as bricks for lining blast furnaces and likemetallurgical equipment which bodies are highly resistant to alkaliattack.

Another object is to provide a refractory body having improvedresistance to alkali attack.

Other objects and advantages of the invention will become apparent as tothe following detailed description progresses.

According to one aspect of the present invention, the lining of a blastfurnace or other furnace operating under reducing conditions consists atleast partly of refractory material, the surface layer of the insidepore surface of which consists partly of a phosphorus compound,-but inwhich the ceramic bond is substantially free from this compound.

In accordance with another aspect of this invention a refractory body,such asbricks for lining metallurgical equipment such asblast furnaceshaving a porosity of at least 10 percent and the grains of said bodybeing held together by ceramic bondings, is subjected to an impregnationtreatment with an aqueous solution of a phosphorus compound and theimpregnated material is then heatedat a temperature above C, preferablybetween 400 C and 500 C for at least 1 hour, preferably 5 to 6 hours.

In this respect it should be remarked that the invention is purposelyrestricted to refractory bodies having a porosity of at least 10percent. It was found that refractory bricks having a porosity of lessthan 10 percent are insufficiently elastic under the conditions in blastfurnaces and like metallurgical equipment, and

will soon crush when exposed to varying temperatures. The ultimatedeterioration of such bricks will therefore not be due to alkali attackin the first place. Also, the smaller the porosity is, the smallerbecomes the internal pore surface, and hence the available surface onwhich alkali attack can take place.

The invention is based upon the discovery that a refractory brick oranother refractory body having a porosity of at least 10 percent whichis substantially completely ceramically bonded is impregnated with anaqueous solution of a phosphorus compound and thereafter heated at atemperature above 100 C for at least 1 hour, results in a product inwhich the impregnated phosphorus compound is only present in the toplayer of the inside pore surface whereas the ceramic bonding of saidrefractory product is substantially free from said phosphorus compounds.Such a product is highly resistant to alkali attack.

The ceramical bond is obtained by firing at such a high temperature (asa rule above 900 C), that from the refractory grains sufficient glassyliquid is formed to bind the more refractory parts of the grains, mainlymullite, together.

Many refractory clays satisfy the general formula (K ,(Al O;,),,(SiO -HO,,. By firing such a clay a transformation takes place into:

SiO (kristoballite) K O-SiO (glass phase) The mullite and kristoballitegrains are molten together with the glass phase.

Although the amount of the phosphorus compounds employed is immaterial,preferably the amount of phosphorus compound which is impregnated issuch that the content of the phosphorus compound, calculated as P 0 is 2percent to 8 percent by weight of the refractory material. The amount ofthe phosphorus compound which is impregnated depends on the porosity andthe pore-size of the refractory material.

The higher the porosity and the bigger the pores of the refractorymaterial the higher also the amount of phosphorus compound which isimpregnated.

Suitable phosphorus compounds for use in the present invention areortho-phosphoric acid (H PO and ammonium phosphate ((NH PO Aluminumphosphates such as mono-aluminum phosphate (Al(H PO (aluminum dihydrogenorthophosphate) and aluminum meta-phosphate (Al(PO are preferred.

The refractory material to be used for the impregnation treatmentaccording to the invention may be selected both from the group of theoxides of aluminum and silicon and the alumino silicates and from thegroup of refractory material mainly composed of carbon.

The invention is also related to the refractory bricks or otherrefractory bodies for lining blast furnaces and like metallurgicalequipment being resistant to alkali attack comprising a porousrefractory body, the refractory grains of which are ceramically bondedtogether, in which the surface of the internal pores contain aphosphorus compound, the ceramic bond, however,

being substantially free from said phosphorus compound.

The impregnation of refractory material with phosphorus compoundsaccording to the invention in order to make this material resistant toalkali attack should not be mistaken for the known treatment ofrefractories with phosphoric acid and/or phosphate with subsequentheating in order to react said phosphorus compound with the refractory.Such a product may have an improved strength due to the improvedcoherence of the refractory grains through chemical bonds; however,these chemical bonds are different from ceramic bonds obtained bybinding the grains of the refractory material together by means of aglassy phase. More particularly such chemical bonds contain phosphoruscompounds, which cause "the strength of the refractory bricks quickly tofall down at elevated temperatures. This can be elucidated by measuringthe strength of a chemically bonded refractory brick at varioustemperatures. One such a brick is traded by the code-name PH 850 and isbonded with a monophosphate compound. At 20 C these bricks show abending strength of 1,400 psi, which increased up to 2,550 psi when thebrick is heated to 400 C, because of a transformation of themonophosphate into a polyphosphate compound. On further elevating thetemperature the polyphosphate is broken down, which results in astrength of 990 psi. at l,200 C, and 630 psi. at l,400 C. On cooling thebrick its strength is not restored.

Contrasted with this known treatment in which the strength of therefractory before and after treatment is essentially increased and thebonding of the material is substantially of the chemical type, there isno significant increase in strength after the treatment according to thepresent invention. According to the invention, the treatment ,is carriedout on ceramically bonded refractory bodies, the strength of which isalmost maximum before impregnation. Due to the fact that the strength ofthe ceramical bonds is not essentially affected by the impregnation withphosphoric acid, phosphorus compounds or decomposition product thereof,said refractory bodies remain essentially unimpaired in this respect. Itis also found that upon firing such a brick up to l,400 C andsubsequently cooling it again, the strength remains essentiallyunimpaired, as contrasted with the chemically bonded bricks.

Although the reason for the surprising effect obtained by the presentinvention is not entirely known, it is assumed that the improvedprotective action of refractory materials treated according to thepresent invention against alkali attack is due to the fact that thephosphorus compounds are bonded to the inside pore surface and form onsaid surface a heat and alkali resistant polymeric framework.

The impregnation of the refractory body can be carried out in differentways but it is preferable to im pregnate the ceramically bonded materialat room temperature under partial vacuum for at least about 30 minutes.

Another suitable method for impregnating the ceramically bonded bodycomprises impregnating the material under atmospheric pressure for morethan about 30 minutes after heating the body at about a temperature ofto 250 C.

To investigate the proneness to alkali attack the following test can beused:

In a section of brick measuring approximately 4 /z X 4 V2 X 3 inches, ahole of 50 mm diameter is drilled to 45 mm depth. Into this hole iscompressed 100 grams of anhydrous potassium carbonate. The brickspecimen or crucible containing the potassium carbonate is thensubjected to heat treatment by placing it in a stainless steel orceramic box, the specimen being surrounded on all sides by crushedmetallurgical coke. The box is then heated to 950 C. in 4 hours andmaintained at that temperature for 5 hours, e.g., in an electricallyheated furnace or in a furnace fired with gas and air.

After the heat treatment, the box is allowed to cool and the contentsare then removed, the coke being removed by a vacuum cleaner or similarapparatus.

Examination of the specimen reveals that the potassium carbonate hasmelted and been partially dissociated. Generally the majority of thematerial has been absorbed into the brick structure. The absorbedmaterial reacts with the constituents of the brick and forms the type ofcompounds of which examples have been give above. This may lead tocomplete disintegration of the brick, or varying degrees of cracking.Depending upon the extent to which the specimen has been disrupted, thebricks are given an index, to indicate their resistance to alkaliattack:

Reference to this crucible test is made below, in demonstrating theeffectiveness of the invention, but many modifications of the test arepossible without affecting its validity. In applying the test, the heattreatment can be repeated on specimens with the addition of furtherpotassium carbonate between each treatment. In this way it is possibleto produce progressive deterioration of specimens, and, for example, arefractory quality having an index of 4 after the first test could havean index of only 2 after the third test. This makes it possible torelate the results of the test closely to the likely performance of therefractory material in service.

Thus, starting with an unimpregnated brick giving an index of 1 afteronly one test, there can be produced a brick giving on index of 5 afterrepeated tests, by giving it the impregnation treatment described above.

The following examples, which are not to be regarded as limitative asregards the application of the invention, demonstrate the advantagesachieved by the invention:

EXAMPLE I An alumino-silicate refractory brick of quality commonly usedas lining material for iron-making blast furnaces having an apparentporosity of 11.1 percent, a

cold crushing strength of 840 kg/cm and being produced by firingalumino-silicate refractory material having the desired shape at atemperature above the vitrification temperature of this material so asto'vitrify the refractory grains together forming ceramic bonds in thebrick, was found to be subject to alkali attack. The brick had thefollowing chemical analysis:

Si0 51.80% by Weight A1 0 44.21% by weight TiO- 1.27% by weight Fe 00.93% by weight Cat) 034% by weight MgO 0.2l% by weight K 0 0.23% byweight Na 0 0.6l% by weight Other elements 0.40% by weight One-half ofthe brick was subjected to an impregnation treatment as described belowin order to introduce a phosphorus containing compound into the pores ofthe brick, the other half of the brick was left untreated.

The impregnation treatment on one-half of the brick was carried out asfollows.

The brick-half was placed in a vessel and the vessel was sealed. Avacuum pump was then attached to the vessel and the pressure reduced to2 inches water gauge. An aqueous solution of orthophosphoric acid havinga concentration of about 50 percent was then introduced into the vesseluntil the brick-half was completely covered. This situation wasmaintained for 30 minutes. Then atmospheric pressure was reintroducedinto the vessel above the ortho-phosphoric acid solution. Theortho-phosphoric acid solution was removed from the vessel and the brickwas found to have their pores completely filled up with phosphoric acidsolution. The impregnated brick was transferred to an electricallyheated furnace and the temperature was raised to 450 C, this beingmaintained for 5 hours. The furnace was then allowed to cool and thebrick was removed. In the following table, the cold crushing strengthand resistance to alkali attack (expressed in the index figuresaccording to the above mentioned crucible test are given for anunimpregnated brick and for a brick after the above mentionedimpregnation treatment.

The index figures before and after the impregnation treatment show thatthe untreated brick is prone to complete disintegration or at least tolight cracking and that such a brick is made wholly resistant to alkaliattack or prone to no more than light cracking when it is treated in theabove mentioned way. The treated brick is thus eminently suitable forparts of the lining of an iron-making blast furnace, by virtue of theirgreatly improved resistance to attack by alkali metal compounds.

After the above mentioned impregnation treatment, the brick was found tohave an apparent porosity of 6.82 percent and a P 0 content of 2.5percent.

Specimens of the above mentioned treated brick were boiled in water butit was found that the impregnated phosphorus compound was completelyinsoluble.

EXAMPLE 2 A ceramically bonded carbon refractory brick of qualitycommonly used as a lining material in the hearth of iron-making blastfurnace having an apparent porosity of 14 percent and a cold crushingstrength of 300 kg/cm was found to be subject to alkali attack. Thebrick had the following chemical analysis:

carbon 95.9% by weight C 1.1% by weight S 0.13% by weight Pb 0.3% byweight Ash 3.2% by weight (containing mainly K20, Na 0 and Sio One-halfof the brick was subjected to an impregnation treatment and to asubsequent heating in the same manner as described in Example I, theother half of the carbon brick was left untreated.

From the following table, the surprising improvement in the resistanceto alkali attack can be seen.

Cold crushing strength Crucible test kg/cm index figure unimpregnated300 3-4 impregnated 300 5 The phosphorus in the treated brick proved tobe insoluble in boiling water.

After the impregnation treatment as mentioned above, the brick was foundto have a P 0 content of 3 percent.

EXAMPLE 3 A ceramically bonded high alumino brick of quality suitablefor lining parts of an iron making blast furnace having an apparentporosity of 21.8 percent, a cold crushing strength of 400 kg/cm andbeing produced by firing high alumina refractory material having thedesired shape above the vitrification temperature of this material inorder to bond the refractory grains together by ceramic bonds, was foundto be subject to alkali attack. The brick had the following chemicalanalysis.

Si0 0.15% by weight A1 0; 97.78% by weight Fe O 0.03% by weight Tit)0.04% by weight Cal) 0.11% by weight Mg0 0.10% by weight K 0 0.02% byweight Na 0 0.17% by weight,

strength Crucible test kg/cm index figure" unimpregnated 400 limpregnated 400 4 The above mentioned test was repeated except that asaturated aqueous solution of aluminum metaphosphate was used instead ofthe aqueous solution of aluminum (ii-hydrogen ortho-phosphate. Afterdrying and cooling the brick was found to contain a content of about 4%P 0 which was insoluble in boiling water. Also the crucible test"rendered the same results.

Again the above mentioned test was repeated, but this time the sampleswere impregnated with a satu rated aqueous solution of ammoniumphosphate.

After drying and coolirigthe brick contained 8% P 0 and the "crucibletest rendered an index figure of 5.

What is claimed is: i i

1. A method for making refractories adapted for lining blast furnacesand the like having an improved resistance to attack by alkali whichcomprises impregnating the pores of a refractory body having a porosityof at least 10 percent and refractory grains which are sub stantiallycompletely ceramically bonded together by vitrification with an aqueoussolution of a phosphorous compound and heating the impregnated body at atemperature above C for at least 1 hour thereby depositing thephosphorous compound on the surface of the pores while the ceramic bondsremain substantially free from the phosphorous compound.

2. A method according to claim 1 in which the impregnated body isheatedat a temperature between 400 C and 500 C for from 5 to 6 hours.

3. A method according to claim 1 in which the refractory body isimpregnated with said solution under partial vacuum and at roomtemperature for more than about 30 minutes.

4. A method according to claim 1 in which the refractory body isimpregnated with said solution at atmospheric pressure and at atemperature between C and 250 C for more than about 30 minutes.

5. A method according to claim 1 in which the phosphorus compound isselected from the group con sisting of orthophosphoric acid,mono-aluminum phosphate, aluminum metaphosphate and ammonium phosphate.

6. A method according to claim 1 in which the phosphorus compound isimpregnated into said refractory body in an amount such that the contentof the phosphorus compound, calculated as P 0 is 2 to 8 percent byweight of said body.

7. A method according to claim 1 in which the refractory body isselected from the group consisting of aluminum oxide, silicon oxide andalumino silicates.

8. A method according to claim 1 in which the refractory body consistsessentially of carbon.

9. A refractory for lining blast furnaces and the like having a porousrefractory body of ceramically welded refractory grains, the porosity ofthe body being at least 10 percent, said body containing a phosphorouscompound on the surface of its pores but being substantially free fromphosphorus compound in the ceramic bonds whereby said body has improvedresistance to attack by alkali.

l0. Refractory body according to claim 9 in which the content of thephosphorus compound, calculated as P is 2 to 8 percent by weight of saidbody.

2. A method according to claim 1 in which the impregnated body is heatedat a temperature between 400* C and 500* C for from 5 to 6 hours.
 3. Amethod according to claim 1 in which the refractory body is impregnatedwith said solution under partial vacuum and at room temperature for morethan about 30 minutes.
 4. A method according to claim 1 in which therefractory body is impregnated with said solution at atmosphericpressure and at a temperature between 150* C and 250* C for more thanabout 30 minutes.
 5. A method according to claim 1 in which thephosphorus compound is selected from the group consisting oforthophosphoric acid, mono-aluminum phosphate, aluminum metaphosphateand ammonium phosphate.
 6. A method according to claim 1 in which thephosphorus compound is impregnated into said refractory body in anamount such that the content of the phosphorus compound, calculated asP205, is 2 to 8 percent by weight of said body.
 7. A method according toclaim 1 in which the refractory body is selected from the groupconsisting of aluminum oxide, silicon oxide and alumino silicates.
 8. Amethod according to claim 1 in which the refractory body consistsessentially of carbon.
 9. A refractory for lining blast furnaces and thelike having a porous refractory body of ceramically welded refractorygrains, the porosity of the body being at least 10 percent, said bodycontaining a phosphorous compound on the surface of its pores but beingsubstantially free from phosphorus compound in the ceramic bonds wherebysaid body has improved resistance to attack by alkali.
 10. Refractorybody according to claim 9 in which the content of the phosphoruscompound, calculated as P205, is 2 to 8 percent by weight of said body.11. Refractory body according to claim 9 in which the phosphoruscompound is incorporated as an aluminum phosphate in said body. 12.Refractory body according to claim 9 in which the refractory material ofsaid body is seleCted from the group consisting of aliminum oxide,silicon oxide and alumina silicates.
 13. Refractory body according toclaim 9 in which the refractory material of said body consistsessentially of carbon.